add AddMissingHeaderRule to check copyright header comments (#142)

* add AddMissingHeaderRule to check copyright header comments

* remove unused import

.fixit.config.yaml

@@ -13,3 +13,10 @@ rule_config:
   ImportConstraintsRule:
     fixit:
       rules: [["*", "allow"]]
+  AddMissingHeaderRule:
+    path: "*.py"
+    header: |-
+      # Copyright (c) Facebook, Inc. and its affiliates.
+      #
+      # This source code is licensed under the MIT license found in the
+      # LICENSE file in the root directory of this source tree.

fixit/cli/tests/__init__.py

@@ -0,0 +1,4 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.

fixit/common/tests/__init__.py

@@ -0,0 +1,4 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.

fixit/rules/add_file_header.py

@@ -0,0 +1,141 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from typing import List
+
+import libcst as cst
+import libcst.matchers as m
+
+from fixit import (
+    CstContext,
+    CstLintRule,
+    InvalidTestCase as Invalid,
+    LintConfig,
+    ValidTestCase as Valid,
+)
+
+
+class AddMissingHeaderRule(CstLintRule):
+    """
+    Verify if required header comments exist in a module.
+    Configuration is required in ``.fixit.config.yaml`` in order to enable this rule::
+
+        rule_config:
+           AddMissingHeaderRule:
+               path: pkg/*.py
+               header: |-
+                   # header line 1
+                   # header line 2
+
+    (Use ``|-`` to keep newlines and add no new line at the end of header comments.)
+    ``path`` is a glob-style ``str`` used in `Path.match() <https://docs.python.org/3/library/pathlib.html#pathlib.PurePath.match>`_.
+    The specified ``header`` is a newline-separated ``str`` to be enforced in files whose path matches.
+    """
+
+    MESSAGE: str = "A required header comment for this file is missing."
+
+    VALID = [
+        Valid("import libcst"),
+        Valid(
+            """
+            # header line 1
+            # header line 2
+            import libcst
+            """,
+            config=LintConfig(
+                rule_config={
+                    "AddMissingHeaderRule": {
+                        "path": "*.py",
+                        "header": "# header line 1\n# header line 2",
+                    }
+                }
+            ),
+        ),
+        Valid(
+            """
+            # header line 1
+            # header line 2
+            # An extra header line is ok
+            import libcst
+            """,
+            config=LintConfig(
+                rule_config={
+                    "AddMissingHeaderRule": {
+                        "path": "*.py",
+                        "header": "# header line 1\n# header line 2",
+                    }
+                }
+            ),
+        ),
+        Valid(
+            """
+            # other header in an unrelated file
+            import libcst
+            """,
+            filename="b/m.py",
+            config=LintConfig(
+                rule_config={
+                    "AddMissingHeaderRule": {
+                        "path": "a/*.py",
+                        "header": "# header line 1\n# header line 2",
+                    }
+                }
+            ),
+        ),
+    ]
+    INVALID = [
+        Invalid(
+            "# wrong header",
+            config=LintConfig(
+                rule_config={
+                    "AddMissingHeaderRule": {"path": "*.py", "header": "# header line"}
+                }
+            ),
+            expected_replacement="# header line\n# wrong header",
+        )
+    ]
+
+    def __init__(self, context: CstContext) -> None:
+        super().__init__(context)
+        config = self.context.config.rule_config.get(self.__class__.__name__, None)
+        if config is None:
+            self.rule_disabled: bool = True
+        else:
+            if not isinstance(config, dict) or "header" not in config:
+                raise ValueError(
+                    "A ``header`` str config is required by AddMissingHeaderRule."
+                )
+            header_str = config["header"]
+            if not isinstance(header_str, str):
+                raise ValueError(
+                    "A ``header`` str config is required by AddMissingHeaderRule."
+                )
+            lines = header_str.split("\n")
+            self.header_matcher: List[m.EmptyLine] = [
+                m.EmptyLine(comment=m.Comment(value=line)) for line in lines
+            ]
+            self.header_replacement: List[cst.EmptyLine] = [
+                cst.EmptyLine(comment=cst.Comment(value=line)) for line in lines
+            ]
+            if "path" in config:
+                path_pattern = config["path"]
+                if not isinstance(path_pattern, str):
+                    raise ValueError(
+                        "``path`` config should be a str in AddMissingHeaderRule."
+                    )
+            else:
+                path_pattern = "*.py"
+            self.rule_disabled = not self.context.file_path.match(path_pattern)
+
+    def visit_Module(self, node: cst.Module) -> None:
+        if self.rule_disabled:
+            return
+        if not m.matches(node, m.Module(header=[*self.header_matcher, m.ZeroOrMore()])):
+            self.report(
+                node,
+                replacement=node.with_changes(
+                    header=[*self.header_replacement, *node.header]
+                ),
+            )